Metal foil lead-in conductor for electric lamp



. Oct. 1, 1963 R. A. J. M. MEIJER 3,105,867

METAL FOIL LEAD-IN CONDUCTOR FOR ELECTRIC LAMP Filed Sept. 8, 1960 INVENOR United States Patent .0

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Filed Sept. 8, 1960, Ser. No. 54,742 Claims priority, applicationNetherlands Sept. 23, 1959 Claims. (Cl. 174-5064) This invention relatesto electric lamps having at least one strip-shaped foil of refractorymetal sealed into quartz or a similar material and having a thicknessgreater in the middle than at the edges.

A material similar to quartz is to be understood herein to mean amaterial having a coefiicient of expansion less than 20x Molybdenum is.usually employed as the refractory metal, but tungsten, platinum,iridium, etc. or, if desired, alloys thereof also enter into account forthis purpose.

The combination used in the majority of cases comprises a molybdenumfoil sealed into quartz in a vacuum.- tight manner.

The foils having a greater thickness at the center permit the passage ofstronger electric current than would be possible with foils of uniformthickness.

It is known for wire-shaped conductors sealed into glass to be protectedagainst oxidation by means of a layer of chromium, nickel, cobalt, iron,thorium, zirconium, platinum, silicon, etc. provided on the Wire.

The use of such protective layers on strip-shaped foils which arethicker at the center than at the edges does not cause any appreciabledifficulty in sealing into glass.

However, when such foils are sealed into quartz or a similar materialhaving a coefiicient of expansion less than 10 it is very difiicult toobtain a seal which is vacuum-tight and oxidation-proof.

An object of the invention is to improve this.

According to the invention, the foil is covered with a metallic layerproviding protection against oxidation, which is such that the core,which consists of refractory metal, has a thickness at the center whichis more than 15 microns and less than 70 microns, and that this corecarries a layer of from 1 to 8 microns thick which has formed byalloying the protective metal with the metal of the core, and thatfurthermore this layer is covered with a layer 0.5 to 4 microns thick ofthe protective metal and/or the oxide thereof and possibly the coremetal, the melting point of the last-mentioned layer being lower thanthe softening temperature of the quartz or the similar material.

In order that the invention may be readily carried into effect, oneembodiment thereof will now be described in detail, by way of example,with reference to the accompanying diagrammatic drawing, in which:

, FIGURE 1 shows one end of a lamp provided with a seal according to theinvention, and

FIGURE 2 is a cross-sectional view of the sealing body, taken along theplane IlII of FIGURE 1.

FIGURE 1 shows a cylindrical wall 1 of an electric lamp of quartz, forexample an infra-red radiator, the

extremity 2 of which is pinched closed about a stripshaped sealing foil3 having secured to it current-supply wires 4 and 5. An incandescentspiral 6, a few turns of which only are shown, is secured to the end ofthe wire 5 which extends into the cylindrical space of the lamp.

As can be seen from FIGURE 2, the sealing foil comprises a core 31 ofalmond-shaped cross-section, an intermediate layer 32 covering thiscore, and an outer layer 33 showing protuberances 34 at the sides.

3 ,105,867 Patented Oct. 1, 1963 In the example shown, the core 31consists of molybdenum, the intermediate layer 32 of amolybdenumchromium alloy having a molybdenum content decreasingoutwardly, and the outer layer 33 of chromium and/ or chromium oxide andpossibly a small percentage of molybdenum. The melting point of amolybdenum-chromium-alloy is usually lower according as the molybdenumcontent is less. Prior to sealing, the foil comprises only the core 31and the layer 32. The high temperature of about 2000 C. which is used informing the pinch, causes melting away of the portion of the layer 32remote from the core 31, which has a melting point lower than that ofthe portion adjacent the core, resulting in the formation of the outerlayer 33, distinctly visible under a microscope, with the associatedthin transparent protuberances 34. During pinching, a proportion of thechromium at the areas 33 and 34 can change to the chromium-oxide givingprotection against further oxidation. As a matter of fact, a littlemolybdenum may also be present at these areas. However, the contentthereof is so small that the said melting away has not been prevented.

The core of the sealing foil having a width of about 4 mms. and a lengthof about 8 mms. in the direction of the wires 4 and 5 is about 22microns thick at the center of the cross-section. It has beenempirically found that this thickness must not be less than 15 microns,since otherwise the foil is liable to tear during sealing. On the otherhand, this thickness must not be more than microns to prevent thevacuum-tightness of the seal from being hazar'ded.

The outer layer 33 has a thickness of about 2 microns. For protectionagainst oxidation, this layer must have a thickness of at least 0.5micron, while for a vacuumtight seal a thickness of at most 4 microns ispermissible.

The intermediate layer 32 has a thickness of about 2 microns. This layermust have a thickness of at least 1 micron to produce a sufficientlythick layer 33, while a thickness of more than 8 microns would hazardthe vacuum-tightness.

In the example shown, the width of the protuberances 34 at the sides isabout 1.5 mms. It has surprisingly been found that this width providesan indication about the qualtity of the seal.

When the protuberances are materially narrower, protection againstoxidation of the molybdenum core is not guananteed, whereas the presenceof protuberances which are materially wider, for example extend to theedge of the pinch, may be an indication of insufiicient vacuumtightnessof the seal.

What is claimed is:

1. A lead-in conductor for an electric lamp comprising a foil sealed ina quartz-like material, said foil having a thickness greater in itsmid-section than at its edges, said foil comprising a core of refractorymetal, an oxidation-protective outer layer surrounding said core, and alayer intermediate the outer layer and the core consisting of a metalwhich is capable of forming an alloy with the core metal and which iscapable of forming a protective oxide, said core having a thickness atits mid-section of between 15 and 70 microns, the outer layer having athickness of about 0.5 to 4 microns, and the intermediate layer having athickness of about 1 to 8 microns, said outer layer having a meltingpoint which is lower than the softening temperature of the quartz-likematerial.

2. A lead-in conductor for an electric lamp comprising a foil sealed ina quartz-like material, said foil having a thickness greater in itsmid-section than at its edges, said foil comprising a core of refractorymetal, an oxidationprotective outer layer surrounding said core, and alayer intermediate the outer layer and the core consisting of a metalwhich is capable of forming an alloy with the core metal and which iscapable of forming a protective oxide, said core having a thickness atits mid-section of between 15 and 70 microns, the outer layer having athickness of about 0.5 to 4 microns, and the intermediate layer having athickness of about 1 to 8 microns, said outer layer having a meltingpoint which is lower than the softening temperature of the quartz-likematerial, said foil having proturberances at its edges constituted bythe material of the outer layer.

3. A lead-in conductor for an electric lamp comprising a foil sealed ina quartzlike material, said foil having a thickness greater in itsmid-section than at its edges, said foil comprising a core ofmolybdenum, an oxidationprotective outer layer surrounding said core,and a layer intermediate the outer layer and the core consisting of ametal which is capable of forming an alloy with the core metal and whichis capable of forming a protective oxide, said core having 'a thicknessat its mid-section of between 15 and 70 microns, the outer layer havinga thickness of about 0.5 to 4 microns, and the intermediate layer havinga thickness of about 1 to 8 microns, said outer layer having a meltingpoint which is lower than the softening temperature of the quartz-likematerial.

4. A lead-in conductor for an electric lamp comprising a foil ofrefractory metal sealed in a quartz-like material, said foil having athickness greater in its mid-section than at its edges, said foilcomprising a core of molybdenu'rn an oxidation-protective outer layer ofchromium surrounding said core, and a layer intermediate the outer layerand the core consisting of an alloy of molybdenum and chromium, saidcore having a thickness at its midsection' of between '15 and microns,the outer layer having a thickness of about 0.5 to 4 microns, and theintermediate layer having a thickness of about 1 to 8 microns, saidouter layer having a melting point which is lower than the softeningtemperature of the quartz-like material.

5. A lead-in conductor for an electric lamp comprising a foil ofrefractory metal sealed in a quartz-like material, said foil having athickness greater in its mid-section than at its edges, said foilcomprising a core of molybdenum an oxidation-protective outer layer ofchromium oxide, and a layer intermediate the outer layer and the coreconsisting of an alloy of chromium and molybdenum, said core having athickness at its mid-section of between 15 and 70 microns, the outerlayer having a thickness of about 0.5 to 4 microns, and the intermediatelayer having a thickness of about 1 to 8 microns, said outer layerhaving a melting point which is lower than the softening temperature ofthe quartz-like material.

References Cited in the file of this patent UNITED STATES PATENTS

1. A LEAD-IN CONDUCTOR FOR AN ELECTRIC LAMP COMPRISING A FOIL SEALED INA QUARTZ-LIKE MATERIAL, SAID FOIL HAVING A THICKNESS GREATER IN ITSMID-SECTION THAN AT ITS EDGES, SAID FOIL COMPRISING A CORE OF REFRACTORYMETAL, AN OXIDATION-PROTECTIVE OUTER LAYER SURROUNDING SAID CORE, AND ALAYER INTERMEDIATE THE OUTER LAYER AND THE CORE CONSISTING OF A METALWHICH IS CAPABLE OF FORMING AN ALLOY WITH THE CORE METAL AND WHICH ISCAPABLE OF FORMING A PROTECTIVE OXIDE, SAID CORE HAVING A THICKNESS ATITS MID-SECTION OF BETWEEN 15 AND 70 MICRONS, THE OUTER LAYER HAVING ATHICKNESS OF ABOUT 0.5 TO 4 MICRONS, AND THE INTERMEDIATE LAYER HAVING ATHICKNESS OF ABOUT 1 TO 8 MICRONS, SAID OUTER LAYER HAVING A MELTINGPOINT WHICH IS LOWER THAN THE SOFTENING TEMPERATURE OF THE QUARTZ-LIKEMATERIAL.